Aptamers, which are nucleic acid ligands capable of binding to molecular targets, have recently attracted increased attention for their potential application in many areas of biology and biotechnology. They may be used as sensors, therapeutic tools, to regulate cellular processes, as well as to guide drugs to their specific cellular target(s). Contrary to the actual genetic material, their specificity and characteristics are not directly determined by their primary sequence, but instead by their tertiary structure. Aptamers have been recently investigated as immobilized capture elements in a microarray format. Others have recently selected aptamers against whole cells and complex biological mixtures.
Aptamers are commonly identified by an in vitro method of selection sometimes referred to as Systematic Evolution of Ligands by EXponential enrichment or “SELEX”. SELEX typically begins with a very large pool of randomized polynucleotides which is generally narrowed to one aptamer ligand per molecular target. Once multiple rounds (typically 10-15) of SELEX are completed, the nucleic acid sequences are identified by conventional cloning and sequencing. Aptamers have most famously been developed as ligands to important proteins, rivaling antibodies in both affinity and specificity, and the first aptamer-based therapeutics are now emerging. More recently, however, aptamers have been also developed to bind small organic molecules and cellular toxins, viruses, and even targets as small as heavy metal ions.